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Why did Boeing never replace the 757?
https://boeing.mediaroom.com/2005-04-28-Boeing-Closes-Chapter-in-Aviation-History-with-Final-757-Delivery

Boeing in late 2003 decided to end 757 production because the increased capabilities of the newest 737s and the potential of the all-new Boeing 787 fulfill the 757 market's needs.

But instead a gap was created in their lineup as this graphics from 2014 shows quite well:

So how did the expectations not pan out? Were they wrong in the first place and have there been significant changes to the 787 before it entered service?

That chart is missing the 737MAX-10 at 230 seats, which perfectly fills that gap.

The earliest studies for the MAX-10 were in 2016. That's some 13 years after the decision to stop the 757.

By the way, why does the chart list the 747-8 for future Boeing aircraft.  Those have already been phased out and the last 747-8Fs are being produced as we speak.

This chart is from 2014. I mentioned that in the question and it's in the footer of the chart too. The 747-8 "died" in 2017 or so.

A replacement for the 757 was planned but canceled, just as the replacement for the 737 was canceled. The funds instead were put into the 787, with some money going to patch up the 737 and 777 into the 737Max and 777X (all of which turn out to be highly problematic).

Do you have any sources of the 757 replacement plans before 2011 when the 787 finally entered into service?

Where did you find that size chart? Do you know if there's a similar chart for Airbus? (or for both Airbus and Boeing?)

The gap happened because the 737MAX wasn’t part of the original plan.
The 767 and 757 shared a type rating and a lot of common parts, and orders had dried up for both, so they didn’t have much choice about ending production. The 737 was getting pretty old too. However, the replacement of the 747 with the 777 was going well, so why not keep going and replace everything?
Boeing’s replacement for the 767 was the 787, which was received very well despite being a radical change. Not only did it quickly kill off demand for the 767, it also started replacing 747s and (oops) 777s.
The next step was to downsize the 787 to make the New Midsize Aircraft (NMA), which would replace the 757 and 737NG.
However, Southwest Airlines(SWA) pushed back hard on having a second type in their fleet (they fly all 737s). If Boeing forced them to do that, they would switch to Airbus. Boeing had to re-engine the 737 or lose their most loyal customer.
So, the folks that were supposed to develop the NMA were shifted to what became the 737MAX.  The MAX9 wasn’t large enough to replace the 757, but that was okay because they were still assuming the NMA would eventually get built, so the gap it left in their lineup (as seen in your chart) was only temporary.
However, the MAX took a lot longer to launch than expected and then the MCAS fiasco cost them a ton of money and goodwill in the market, so rather than lose a decade launching the NMA into that gap, they did another cheap hack to the 737 (since that went so well the last time) to produce the MAX10.
Now that the hole in the product line is closed, there’s no longer a clear market segment for the NMA, so it was canceled for good.

Very interesting. SWA became the launch customer of the 737 MAX in 2011 Dec and it's hard to find information on what went on before. Do you have a source for SWA pushing Boeing away from downsizing the 787? I found some references to a 787-3 https://simpleflying.com/boeing-787-3-nma/ which apparently had some orders from Japanese airlines but this article claims it got mothballed because the first Dreamliners were late and doesn't mention any SWA resistance.

https://www.seattletimes.com/business/boeing-aerospace/legal-filing-reveals-southwest-airlines-proposed-a-ploy-to-deceive-faa-on-boeing-737-max/ this article certainly seems to indicate SWA had a huge influence on the 737 MAX.

@chx NMA wasn’t just a short 787; it would use the same tech but with a smaller elliptical fuselage, shorter wings and smaller engines. And yes, SWA absolutely is the reason MAX happened. That is well documented.

I can see that but I can't find them pushing back on the 787, that'd be very interesting to read about.

@chx They pushed back on the NMA, not the 787.

I am looking for exactly that: the history of an early NMA. There was something -- you are saying so and this mysterious forum post from 2005 says "
They do have it on the 'back burner'. After the 787, Boeing's next big project will be a new narrow-body family that will have a capacity between 125-225 seats, replacing the 73G, 738, 739, and 757-200."

@chx I thought I read about it at the time, but I also know a lot of pilots at SWA and AAL who might’ve shared details that never made it to the media, so maybe not?

Let us continue this discussion in chat.

Do you have a source on an intent to replace the 737 with NMA? My understanding was that NMA was more to replace the 757 and maybe the MAX 10, not the whole 737 family. I thought NSA (New Small Airplane) was/is supposed to be the successor to the 737.

It was called the Boeing Y1 and yes it was intended to replace the 737 and 757-200, the last time Boeing said they will do it was in 2011 May and in 2011 December the 737 MAX was announced with SWA ordering a ton of them. I am piecing together the story right now.

Ah, I'm not sure on that timeline. Was it not that a major US airline was about to buy A321s that forced Boeing to paper launch the Max? The original plan being NSA, not NMA.

That's what @StephenS says too but -- sources? The original plan almost surely was the Boeing Y1 back then it wasn't called NSA/NMA was as far as I can tell.

The 737 MAX 10 is the replacement, for now. It almost matches the 757-200 on capacity (230 vs 240) and the 757-300 on range (3300 vs 3400 nmi), while staying considerably lighter and cheaper, due to being based on a scaled-up regional design.
Boeing had plans for a New Midsize Airplane, but these got delayed and possibly canned when the pandemic started.
A lot of awesome things were expected from the NMA, like a true light two-aisle design (2-3-2), with the comforts of a widebody, but not fitting the cramped 3-3-3 787 configuration. With cheap oil and many passengers willing to pay for comfort, its future was looking bright. Its main sacrifice vs the 767 would've been the ability to transport freight. Note that this was speculation, not confirmed specs.
Now, with air travel reduced by the pandemic, then suppressed again, and oil to stay at a new high for a long time, building a new airliner, especially one that doesn't prioritize seat-mile cost as much as possible, looks like a losing proposition economically.
The A320neo largely fills the former 757 role, and competing with it across all segments would take a new design with all associated costs.

The Max 10?  It’s a crappy replacement but, yeah, fits all the criteria for that market niche.

@CarloFelicione Deliberately crappy, I'd say. But in a Walmart kind of philosophy, it's the cheapest thing that only-just-fits the reqs...

Boeing is the Walmart of aviation.

Then, I guess, the question becomes: why did it take thirteen years from the decision to stop the 757 to begin the studies on its replacement?

@Jpe61 Sadly the company sold itself out to those instincts and is rapidly being eclipsed by Airbus.

@chx one of the difficulties in aviation is that trends are sometimes difficult to anticipate, and development of airliners takes a long time. Not to shame Boeing only, Airbus has had its woes too: they had to redesign what became the A350, as their original concept was rejected by carriers. And the A380 was, if not a disaster, not an exact success story. The market for superjumbos melted from under it.

Did you mean the A321neo rather than the A320neo? Also, the NMA delays had a lot more to do with the 737 MAX problems (and 777X problems) than with the pandemic, AFAIK. Its future was already uncertain even before the pandemic. The design resources were not freed up for it nearly as soon as they'd hoped.


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Do military aircraft overflying other countries' airspace require special clearance?
Is there any special clearance, when military aircraft will overfly other countries' airspace? Are they continuously monitored?

You might find the Treay on Open Skies interesting.

@Alex AFAIK, that's just related to flights for surveillance purposes, though, not for, say, flying armed nuclear bombers through another country's airspace.

In general, a diplomatic clearance is required for overflight of military aircraft over other countries. The aircraft are considered state aircraft and prior clearance has to be obtained through diplomatic channels. Note that the clearance is usually issued by the defence ministry of the concerned country.
The mode of clearance and monitoring varies from country to country. In case of US:

Foreign governments seeking diplomatic clearance for state aircraft to transit U.S. territorial airspace or land in the United States must obtain a diplomatic clearance number (DCN) issued in advance by the Office of International Security Operations, Bureau of Political Military Affairs (PM/ISO), Department of State. The DCN authorizes the aircraft to transit or land in the United States and/or its territories, in accordance with the approved itinerary.

The overflight permissions are also dependent on agreement between various countries, like India-Pakistan. In some cases, like some EU countries, military transport aircraft can operate without diplomatic clearance.
Some other countries, like Canada give blanket clearance for military aircraft from some countries:

3.2.3 Blanket Diplomatic Clearances to Foreign Military Aircraft

By order-in-council, United States, United Kingdom, and New Zealand military aircraft are exempted from the requirement to have a formal diplomatic clearance (see 3.2.1 above) prior to overflying and/or landing in Canada.

Military aircraft from North Atlantic Treaty Organization countries other than the United States and the United Kingdom are granted clearances on an annual basis. These clearances do not apply to aircraft carrying armed soldiers, armaments and/or other dangerous goods, nor do they apply to aircraft carrying government personnel.

The procedure is usually the same in most of the countries- the overflight request is given through diplomatic channels to the countries' defence ministry, which then evaluates it and approves (or rejects it). The procedure for Canada is given here:

The state of origin will provide full flight details, as outlined in Annex A, in a diplomatic note from its embassy to Foreign Affairs and International Trade Canada (DFAIT). DFAIT will consult with the Department of National Defence (DND) Operations Centre and, if the foreign military aircraft is landing at a civilian airport, with the Foreign Inspection Division to determine whether any pre-conditions should be imposed. After this consultation, DFAIT will reply to the requesting embassy by a return diplomatic note. On advice from DFAIT, the DND Operations Centre officer will then issue the appropriate flight clearance and distribute copies to the interested parties.

In case of India:

For clearance of flights by foreign military aircraft, the concerned diplomatic mission in India or abroad are required to apply to the Ministry of External Affairs with copy to Air Headquaters/Naval Headquaters forclearance of such flights. After clearance given by Ministry of External Affairs, Air Hqrs/Naval Headquaters will issue necessary AOR number for operation of such aircraft, whether it is overflying Indian air space or landing at any Indian airport (civil or defence).

The monitoring of overflying aircraft depends on the country. Civil ATC usually monitors the aircraft carrying transponders, while the military radars (where available), monitor all air traffic and scramble fighters when the aircraft is not identified/responding properly. Overflight without permission may at the very least result in the aircraft being forced to land by authorities.

In Switzerland, every aircraft is monitored by the air traffic control (ATC). However, if the plane flies without a transponder, it's an unknown aircraft for the ATC-Radar and the military will take the necessary steps to identify the aircraft. Head over here for more details.
At the WEF (World Economic Forum), politicians from all over the world visit Davos. Most of them fly with jets from their air force. Look at this question about the Boeing E-4B Advanced Airborne Command Post 'Nightwatch', carrying Ashton Carter to Switzerland.
From Diplomatic Clearances in Switzerland:

Foreign state flights over or into Switzerland require special permission, known as diplomatic clearance. This permission is granted by FOCA in consultation with other federal offices.

and

State flights include flights engaged in missions undertaken by government, military, customs and police authorities. They particularly include flights by order of the state, flights used for transporting heads of state and high-ranking government officials on official duties, flights used in police and customs operations, and all military flights.

You can find more information about this in the link provided. Keep in mind, this applies only to Switzerland.
These flights often get intercepted and identified by the swiss air force.
Here is a video showing two F5E Tiger II intercepting the Canadian prime minister as he leaves Swiss air space after the WEF 2016

@RonBeyer Thank you. Invisible wasn't the correct word to describe an unknown aircraft on the atc radar. I corrected that.

About the video: Won't the airliner get TCAS RA? Or fighter jets fly with transponder off? But then they are almost invisible.

@Andrius Take a look here: http://www.airliners.net/aviation-forums/tech_ops/read.main/253938 I think the crew gets informed by the atc that they are about to get intercepted. I don't know if the fighter jets fly with or without transponder. Maybe it depends on their mission but you can't see them in switzerland on sites like flightradar24.com, which says to show all aircrafts with transponders - that means they often fly without one, but I'm not 100% sure about this.

UK Tornadoes don't have TCAS, a fact which the Scottish government periodically complains about on safety grounds: http://www.bbc.co.uk/news/uk-scotland-highlands-islands-31023493

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How do the cabin noise levels of the A380 and the 777 300 ER compare?
I couldn't find any official comparison for noise level (dB) in Airbus A380 versus the Boeing 777 300 ER. Does anyone have some info about it? Which one is better in terms of acoustic isolation?

Are you asking for external noise or internal noise?

@SMSvonderTann Internal Noise caused by external causes like engine, airflow, etc.

From a luxury round the world flight on several different models of aircraft on several different airlines, a traveler used the exact same sound meter at his seat in either business or first class to measure ambient noise level during cruise.
Here is a chart I made of his measurements, including carrier and age of aircraft. As you can see, long haul aircraft are quieter than short. Carrier and age of aircraft also seem to make a difference.
For this set of measurements, the b773 is 3db (or 25%) louder than the a380.

Yay, actual data! The question needed that. One correction, 3dB is 41% louder objectively, about 30% subjectively (but depending on frequency). Perhaps the most important 777 vs A380 difference is in economy, though.

@Therac DB gets tricky. You are correct that 3db is 40% greater sound pressure, but it is only perceived as 25% louder and it contains twice as much energy. So you can say 25%, 40% or 100% and be correct in some way. I chose perception as that is the point of the question.

As a passenger:

In the forward bulkhead section of economy class (lower deck) there is almost no engine noise in the A380. If you listen carefully, you can hear it. I was actually surprised at how quiet it was that I didn't need my noise cancelling headphones. In the upper deck, there is no engine noise to speak of.
In the forward section of the 777 (normally this is business class) the noise is a loud but muffled (think of a speaker under a pillow), but not as loud as in the entire economy class cabin. In economy class the noise is atrocious on the 777.

Note that both flights were on Emirates.

The noise levels also depend on the speed the captain is flying, is he cruising normally or is he flying faster to make up time

I can tell you that in economy, the 777 noise was, in my opinion, almost unbearable. The A380 was almost silent. I have been on both on long haul to the uk, and their is a world of difference in the noise levels. Will never fly 777 again.

Where were you in the A380?  My wife and I were on the bottom deck just a couple of rows from the back on Qantas inaugural A-380 flight SYD to SFO and the noise was higher than any other aircraft I can remember. When we questioned a flight attendant about it, she said that the noise level varies greatly depending on whether you're on the top deck or the bottom deck and where you are from fore to aft, and that we were in the very worst part.

@Terry, interesting. I flew on A380 many times, but always on the upper deck (both business and economy, i.e. front and aft). And always found it incredibly quiet, a level of difference from any other airliner. Maybe on the lower deck things are not as stellar...

This is a very difficult question to answer, but lets assume that you're flying during cruise, eliminating as much airframe noise as possible (landing gear, flaps, slats and spoilers) then the position of you in the aircraft is of importance as well. The further you go to the front the more silent your flight will be. Since the A380 also has an upper deck this will be even more silent. Then during the flight it is important to know if the crew is doing some catching up so flying faster than normal, this will indeed be more noisy.
So with this I can give you only my opinion and then overall the A380 is a bit more silent on board, further more I found it harder to notice that we were in fact flying than in the 777. Every movement feels more dampened which contributes to the overall feel on board.
In business class the 777 is more quiet than the 787 in business class when the crew is making up for lost time by flying at a higher speed.
To conclude:

It greatly depends on your position in the aircraft, aft equals more noise
Cruising speed, higher speed than normal equals more noise
Engine type, airlines have for most the option to choose between 2 or 3 engine manufactures.
Personal perception, during the night you're maybe less tolerant to noise than during the day and during the night there is less noise from the cabin to muffle the engine noise.

Anyone who uses the word "silent" relating to a jetliner  has never been on a Superliner.

In my recent travels, I have been lucky to get a host of aircrafts.
777-300ER X 2 (9W)&(SIA), A330-300 X 2 (QANTAS), A350-900 X 1 (SIA), A380-800 X 2 (SIA) seated at various positions. I must say that the A380-800 is a class apart! take a bow Airbus! I had always been partial to the Boeing, but the A380 had taken my heart away. I was seated at the lower deck the 1st time I boarded an A380. Honestly, I had no clue when the aircraft was at rotate speed and through out my 6 hours in it, I could virtually feel no sound at all. Note that I was at the front aft of the economy section. I could enjoy a great view of the Changi airport while the A380 banked almost 360 during a summer sunset. I surprisingly found no difference between the noise levels of the 777-300ER & the A350-900 (shocked) I was rather hoping to find the same db levels on the A350-900 as the A380-800 since conceptually it was a newer aircraft but was bitterly disappointed.
On my way back I was at the upper deck and re-lived that experience of a virtually noise free cabin! Thank you Airbus and thank you Singapore Airlines.
My next would be an A380-800 on Qatar airways! Looking forward to it already.
-Nik

I have just returned B/Class from the UK and both the 380 and the 777 were used.
The 777 for 14 hrs and the 380 for 6hrs.
The difference between the two aircraft was amazing the 380 noise levels are only a quarter of the 777, in the 380 ear plugs were not needed however in the 777 you did plus the audio head phones further reduced the noise in the 777 was unbearable and sleep was not at all possible.

Not a frequent flyer but I've done quite a few SYD-LHR-SYD flights over the years (all economy). No matter the carrier (SIA, BA, EK) the 777 regardless of model is my least favourite thing to fly on - the noise just does not stop and it isn't a pleasant noise either. Give me an A380 any day or night.

It could be nice to find a survey made among passengers to support your point of view. Usually answer focus on objectives measures (which are totally valid) but not on passenger's feelings (as your answer does) on this website. A link to a survey could be a valid option to add passenger's feelings in an objective way.

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What does the abbreviation "SCMOH", related to an engine overhaul, mean?
Scrolling through controller.com. I noticed this, "121.3 SCMOH". Does anyone know what this means?

The C refers to "Channel Chrome" (SCMOH = Since Chrome Major Overhaul), a plating process used to restore worn-oversize cylinder bores. What they do is electroplate the cylinder bores to bring the bore dimension into spec, then reverse the process a little bit, just enough to get de-plating started.
The de-plating causes chrome start to be removed as a web of fissures, that would eventually spread to the entire surface area if it wasn't stopped as soon as the initial fissures form.  You then end up with a surface like the cracked mud of a dry lake bed, at the microscopic level.
The web of microscopic surface fissures act like little ditches where oil is collected and retained for lubrication of the cylinder walls, because the basic chrome surface is too smooth (a normal cylinder has micro-grooves created by the honing process) to retain sufficient oil to lubricate the piston rings.
Chrome has significant plusses and minuses, and always refers to rebuilt cylinders, so if an engine has chrome jugs it's important to advertise it up front right in the acronym.  The cylinders have orange paint on the fins around the spark plugs to denote channel chrome.
On the plus side, chrome bores are long lasting and eliminates cylinder wall corrosion if the plane sits a lot.  On the downside, they take forever to break in, and the oil burn will be higher than steel, nitrided or ceramic-nickel cylinders (I prefer ceramic-nickel).  A lot of people will avoid an engine with chrome cylinders.

This is an excellent question -- but it should be just that: a separate question. Click the [Ask Question] button in the upper right of this page to ask a question. Note: you might want to broaden the question a little to include tire pressure and any other simple maintenance tasks you can think of.

Way beyond that.  The owner can do a lot of stuff, changing oil, and a lot of other light maintenance.  There is a list somewhere on the FAA website.  In Canada you can register your airplane as "Owner Maintenance" and do everything, including inspections, repairs, overhauls, use uncertified parts, as if it was a homebuilt.  You have to X out all the serial #s and the airplane can't leave the country because nobody else recognizes the category, so most owners leave it in normal category.

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Why do jet engines use kerosene rather than gasoline?
Could you run a jet with gasoline? Why do all jet engines use kerosene?

Posting a comment because I only have a partial answer: "The PT6A engine is approved for operation with all commercial jet fuels, JP-4, JP-5 and for a maximum of 150 hours during any overhaul period with all grades of aviation gasoline. Specific grades of diesel fuel are approved as alternate fuels for restricted use."
http://www.pwc.ca/files/en/Know_your_PT6A.pdf

A better question is why do cars run on petrol rather than kerosene.

Cars run on petrol or diesel (which is similar to kerosene). As both are piston engines, the differences are quite big, e.g. diesel engines have twice the compression of petrol engines, different ignition and so on. You can not run the one with the other fuel. But it is not so clear why it's different for jet engines.

@sweber the ignition for jets is different (spray into already ignited chamber rather than compress into piston)

Of course. I mean: For piston engines, there's a big difference between petrol and diesel. However, it seems to be no big difference if you spray kerosene/diesel/petrol into an already burning flame. So, while the difference for piston engines is obvious, it is not for jets. We already know, the PT6A takes avgas and kersosene. So, I don't understand Arons comment.

Every time I hear people say "kerosene" as jet fuel it just seems weird.  I grew up on a farm; I know what kerosene is.  It's the stuff you put in a lantern so you can see to go out and milk the cow at night.  It's much less volatile than, say, gasoline.  It burns slowly and (relatively) cool, which makes it great for a lantern, but--I would imagine--horrible for motor fuel.  Is this a different type of kerosene?

@MasonWheeler it's the same stuff (take a look at the third paragraph)

@raptortech97: So why is something that--at first glance at least--seems to be a much lower-quality fuel than gasoline used in an application that poses a much higher energy demand than even the heftiest gasoline motors face?

@raptortech97: I didn't say energy density.  I said that the energy demand (the required output) is much higher for aviation than for ground transportation, so why use a lower-density fuel? That seems inefficient.

Military turbine engines are designed to operate on everything from avgas to heating oil but are optimized to run on JP4 / JP5 (roughly the weight of kerosene).  If you use one of those other fuels, the engines will require extensive maintenance afterwards.  Jet fuel does have a higher energy density than gasoline: http://en.wikipedia.org/wiki/Energy_density#Energy_densities_of_common_energy_storage_materials

@raptortech97 - Jet fuel does have a slightly higher energy density than gasoline, both by weight and by volume: 46 MJ/kg and 37.4 MJ/l versus 44.4/32.4 for gasoline (and 48/35.8 for diesel fuel)

@Johnny thanks for the correction. I really need to stop running my mouth so much

@MasonWheeler They're planning to make paraffin (candle wax) rockets; the stuff in a match head is just as incendiary bombs in the military. Just because something looks innocent, doesn't say it is in all applications. A lantern can burn for hours - imagine that energy being released (with)in seconds.

@Johnny Looking on the web gives me all kinds of different specific energy #'s. This site shows gasoline at 45.8 and kerosene at 46.3, but jet fuel lower at 43.3.

This site shows the same #'s. This site shows several different numbers from different sources. They all seem to show a different - and lower - number for jet fuel than for kerosene.

@MasonWheeler: Liquid kerosene burns much more slowly than liquid gasoline.  It also has a much lower vapour pressure and much higher flash point than gasoline.  When sprayed as a fine mist into what is essentially a raging fire, it burns just as fast and as readily as gasoline.  Thus, kerosene works just as well as jet fuel as gasoline would (actually, it probably works considerably better, due to its lower vapour pressure, and thus lower boiloff, reducing fuel losses), and is far safer to handle to boot.  Trying to use gasoline for an airportfull of jets would be hideously dangerous.

I'll note that if the FBO accidentally puts AVGAS in your turboprop you will likely be able to land under power. Turbines will burn gasoline. They won't like it and you're looking at some expensive maintenance when you land but you can fly on it. Gas piston engines, unfortunately, just quit running entirely when fueled with Jet-A.

You can persuade a turbine engine to run on just about anything that can burn. So the decision of which fuel to actually use depends on the side factors including, but not limited to:

availability
cost
emissions
hot section temperature
chemical reactions with engine parts

Specific examples:

Coal dust is rather difficult to pump around, and the rampies don't like shovelling
liquid hydrogen (used in the Space Shuttle) requires a lot of storage and has the nasty habit of freezing anything it touches, like rampies.
ethylacetylenedecaborane is unpleasantly toxic (rampies union again) and the combustion byproducts were rather abrasive to the engine's innards
trimethylaluminum would reduce the engine complexity (no igniters needed) because it has the nasty habit of igniting instantly upon contact with air, so leaks are rather dangerous.
natural gas is commonly used as a turbine fuel in pumping stations: it's already there and thus is "free". The required pressure vessels make it impractical to use as an aircraft fuel.

So kerosene basically became the standard turbine fuel because it's:

cheap: kerosene makes up a rather large fraction of crude oil. When you measure your fuel load in tons a few cents per litre makes a difference.
safe to handle: relatively non-toxic, doesn't ignite all that easily
storable and transportable in common structural metals
doesn't clog up the engine

Couldn't turbines just run on rampies ?

The larger engines have been known to snack on them occasionally.

Makes a change from birds I suppose. Pity that the environmentally-friendly free-range bird fuelled jet engine hasn't really had much success.

Industrial gas turbines can and do run on just about anything. There's a stream called "refinery gas" which translates to "anything lighter than pentane that the refinery doesn't want & can't store". This includes hydrogen, carbon monoxide, and hydrocarbons. Frequently they are mixed with inerts like nitrogen (mixtures of hydrocarbon and nitrogen are a pain to separate.) The same turbine will be expected to run on kero or gas oil when that is in excess, or for startup. Water is also injected for NOX control. The only issue, as you say, is not to leave a solid residue that will clog the engine.

@NobodySpecial : Give me some rampies too, I love all kinds of pies... A tad more serious: Is kerosine really used as a lubricant? I heard this the first time but it sounds logical.

@PatricHartmann -- Kerosene and diesel need to have lubricity properties to keep the high-pressure fuel injection pumps in compression ignition (gas turbine, diesel piston) engines from falling apart -- they can't be oiled otherwise!

Perhaps nice to mention why piston engines are so picky: gasoline should only ignite when you hold a spark to it; diesel should ignite immediately when it's sprayed into a hot cylinder. In a jet engine, fuel is sprayed into apocalyptic burning conditions anyway, so one can have a less 'picky' fuel.

@sanchises: Gasoline is easier to ignite than diesel or kerosene. The reason spark-ignited engine can only run on gasoline is that the spark would not ignite the heavier fuel at all or it would burn too slowly. In the compression-ignition engine the temperature is much higher so it ignites even diesel. Incidentally this also increases the thermodynamic efficiency (which is why diesels have about one third lower consumption than gasoline engines).

@UnrecognizedFallingObject : Thank you very much for clarification! It does make sense now, I just never had really though of this issue. Thanks for making this clearer.

What's a rampy?

@MarcusJ slang term for ground crew; i.e the guys who load and unload the planes, fill them with fuel, etc.  on the ramp (or apron, depending where in the world you are)

I see, I'm 'Murican, just never heard that term before, but I don't know too much about aviation or airports, but I'm interested. :)

I thought the biggest problem with coal dust as a turbine fuel was that it produced ash that damaged the blades.

In a modern turbofan engine, fuel is not only burned in the engine and used to lubricate parts such as fuel pumps and controls, it is used as a hydraulic fluid as well -- this is used to power things like inlet guide vanes and variable stator vanes in many engines, as well as more exotic accessories such as movable nozzles and inlet ramps.
This means that gasoline is often not tolerated by larger aviation turbines, as it boils at such a low temperature that it could boil off inside fueldraulic (or other fuel system) parts and interfere with their operation, atop the lubricity and lead fouling issues that it obviously would pose.  Even wide-cut jet fuels such as JP-4 and Jet-B are prohibited for service in some larger turbofans due to the volatility issues they pose (this is a quote from the 777 QRH Limitations section):

The use of JP–4 and Jet B fuels is prohibited.

From my training, the limits on the PT6 use of avgas is related to its ability to lubricate the engine's fuel pumps, and the lead fouling of the hot section  which will result from the avgas. I can't say about other engine's tolerances, but some military jet fuels have much more volatile components than straight kerosene and marine gas turbines run on diesel. A turbine's fuel isn't always decided by what it can burn, but by what it's practical and economic to feed it.

Apologies if this is tangential but other properties of kerosene (aka kerosine) as turbine fuel were brought up.  To my knowledge, all "Jet fuels" (intended for aircraft use) are based on kerosene.
Another property of jet fuel that was not mentioned is freeze point where viscosity drops because of wax formation and pumps and filters begin to clog.  Ordinary kerosene (as used in lanterns and space heaters) rarely has to deal with sub-zero temperature (e.g. -40C) and 30,000 feet altitude.
Also important is volatility which can be reduced at low temperatures and impede combustion.
see http://www.shell.com/global/products-services/solutions-for-businesses/aviation/shell-aviation-fuels/fuels/types/civil-jet-fuel-grades.html for different fuels and their freeze points.

We ran Olympus Gas turbines for fast power and speeds when I was in the Royal Navy. These happened to be the same turbines that Concord used when she was in service. We ran them on Marine Quality Diesel and had no problems.
Again may be its the - temps could be a real issue, and the fact you get more power from Higher octane fuels, with all the technology these days you would think their would be a cheaper alternative.

Compression-ignition fuels (at least in diesels) are rated by cetane -- as anyone who's had Jet-A put in their avgas drinker will tell you, Jet-A has exactly 0 octane rating!

fantastic info!

The very high temperatures of jet engines cause gasoline to be a poor fuel because it tends to burn too fast.  Kerosene, which is routinely called "Fuel OIL" some places, avoids pre-ignition problems (and some safety hazards) just like higher-octane gas avoids spark-plug knocking.  The ultimate control of ignition comes from using Diesel Fuel (which ALSO is routinely called Fuel Oil some places), and that's why big trucks use Diesel: that control gives them the best fuel efficiency their engines can have; but Diesel wont' run a jet engine.  Gasoline is too volatile for a jet engine; Diesel fuel is not volatile ENOUGH for a jet.

The problem with running diesel in a jet engine is the igniters -- the SR-71's triethylborane system would ignite diesel no problem!  (Diesel won't work in the SR-71 through its envelope for various other reasons, but the ignition system in that aircraft isn't one of them, and I suspect a J58 would run on diesel in an emergency, albeit with a severely limited flight envelope.)

Gasoline's extreme burn rate makes it a poor fuel for a much simpler reason: the difference in burn rates is even more conspicuous in the liquid fuels.  A flame will spread over the surface of a pool of gasoline something like six times as fast as over a pool of kerosene, and gasoline also has a much higher vapour pressure and a flash point below most normal ambient temperatures (!).  Even Jet B, which is a mixture of kerosene and gasoline, has safety problems due to gasoline's overenthusiasm for catching fire; pure gasoline is far too dangerous to use as jet fuel.


text:
How do aeroplane wings work?
I wonder why this question has not been posed on this forum.
Is it such a dumb question that nobody needs to ask because the answer is obvious?
A search on the internet for "How do wings work" yields millions of hits, each one bafflingly different from the next.
I would have thought that any answer would include a working example, a simple back-of-the-envelope set of calculations that show that applying real life numbers to the offered theory would show how it works. After all, that's how most science works. You have an idea, you put numbers to it and then see if it works out in practice.

That's how Kepler demonstrated his theory of planetary orbits.
That's how Boyle demonstrated the relationship between the pressure and volume of a gas.
That's how modern physicists used Einstein's theory to explain the variation in the orbit of Mercury.
Whether or not Galileo actually used different sized canon balls to
demonstrate his theory is open to debate.
That's how the Michelson-Morley experiment disproved the theory of
Ether

The list goes on and on.
The scientific process follows a well-worn path:

A theory is developed to explain a physical phenomenon
The theory is developed into a mathematical equation
Numbers are applied to the theory,
Experimentation demonstrates the validity of the theory.

Further experimentation maybe supports the theory, disproves the theory or demonstrates the limitations of the applicability (Newton remained unchallenged until modern physics started to investigate domains beyond human experience, of the very fast, the very heavy or the very tiny.)
Amongst the myriads of explanations for how wings work there appear to be two major competing theories: one invoking the Bernoulli principle to explain the pressure variations around the wing which generate the force and one relying on the momentum change of the disturbed air to account for the aerodynamic force, the vertical component of which balances the weight of the aircraft.
In my search for an answer, I have been unable to find any even "back-of-the-envelope" calculations, using the mathematical equations derived from the theory, real-life numbers and experimental data to support any of these theories.
Is there any paper, journal of textbook which offers a theory and supports it with worked example using real-life data?
For example, one which could demonstrate how a 1-tonne Cessna 172 remains in straight and level flight at 5,000 ft above the ground at 100 kts?
(And I mean a theory that does not rely on a look-up table of Cl/Cd values)
[EDIT]
Since posting this question It has been pointed out that two similar questions have already been posted:
How do wings generate lift? (12 answers)
How complete is our understanding of lift? (9 answers)
Both of these posts generated much discussion but contained no worked examples to support the various claims.
As noted in my question, Physics is an experimental science where the validity of a theory is supported by experimental evidence that real-world numbers applied to the theory correspond to the experimental results.
My question, whilst on the same subject, presents a specific request for a worked example.

To add something to the already given answer: Bernoulli and downward push of air are not competing explanations, they both stem from the 2nd and 3rd Newton principle aka momentum conservation, they are two sides of the same coin.

Why the downvotes? The question is valid and well argumented. The current answer is very interesting.

I submitted and edited version for review 6 days ago. What's the status please?

I think your fundamental premise is unfortunately false.
Kepler's laws were purely empirical.  He had no actual theoretical basis for them.  He used a tremendous amount of data (thanks to Tycho Brahe) and essentially observed the trends.  He just happened to be correct.
Somewhat amusingly (at least to me), beyond Kepler's three laws that we celebrate today, Kepler believed in a fourth law that was absolutely not correct.  He was equally confident in the fourth law, but we virtually erase it from history because it wasn't correct.
There is no simple back of the envelope calculation for a modern physics based deviation in Mercury's orbit.
Many physical phenemona do not reduce down to an elementary algebraic equation.
Aerodynamics -- including the generation of lift -- is very well understood.  It has also been validated through experiment (many wind tunnel tests and flight tests) where the theory and experiment are in very close agreement.  In fact, we have several approaches to the development of the aerodynamic equations -- depending on the assumptions and simplifications we wish to make.
Engineers have a very good understanding of how these levels of theory compare and which are better / worse at predicting reality in different situations.
The issue at hand is that the fundamental theory of aerodynamics does not boil down to a simple equation with immediately obvious physical interpretation.
Everything in aerodynamics can be explained in terms of (and rigorously derived from):

Conservation of mass
Conservation of momentum
Conservation of energy
Gas equation of state
Some other gas relations like the dependence of viscosity on temperature

These five things are intuitive, observable, testable, etc.  There are multiple ways to get from these five things to aerodynamics....
Unfortunately, they are not simple algebraic equations.  Instead, they are a coupled system of nonlinear partial differential equations (1-3) (with some algebraic equations thrown in (4,5)).
The 'modern' way uses the least mathematical abstraction.  It is called CFD (computational fluid dynamics).  In CFD, we divide the domain of interest into a large number of tiny elements.  We initialize all of the elements to an initial guess (that is wrong).  We then solve the above equations on every element, applying appropriate boundary conditions.  This makes a small correction to the properties at every element.  We then do it again, and again, and again....
CFD is a very brute force approach with very little mathematical abstraction.  After millions and millions of calculations, if we're lucky, the properties in all of the elements stops changing (there is theory on how this should happen too).  We then say that the solution is converged.  We can then sum pressures and shear to get lift and drag, we can produce beautiful images of the flow, etc.  We have 'solved' the flow.
Although CFD is very powerful, it is not very satisfying in terms of intuition (which is what you're after).
There are other ways to attack aerodynamics (and the calculation of lift).  You mentioned Bernoulli's equation -- Bernoulli's equation is most frequently derived from the conservation of energy, but it also can be derived from the conservation of momentum.
Potential flow theory (which most pre-CFD low-speed aerodynamics theory was based on) is usually derived from the conservation of mass -- but can also be derived from the conservation of momentum.
Potential flow theory allows aerodynamic calculation with much less brute force than CFD -- but instead, it adopts a great deal of mathematical abstraction.  Complex variables (imaginary numbers), a potential function, sources, sinks, and vortices (mathematical singularities), superposition of elementary solutions, etc.
All of this can be rigorously derived from the fundamental equations -- and all of it has been validated through comparison to experiment.  And more than 100 years of successful application to the design of aircraft.  Engineers have deep understanding of their applicability and limits.
Unfortunately, although all of this is true, it does not mean that it can be explained in one or two sentences without heaps of math.
Any simple explanation of lift is wrong.
Any rigorous and correct explanation of lift is going to get messy.

+1 for Any simple explanation of lift is wrong. -- This should be engraved on the lintel of every flight school in the world.

"Unfortunately, although all of this is true, it does not mean that it can be explained in one or two sentences without heaps of math." I'm not deterred by heaps of maths or an explanation that takes more than a sentence or two. My problem is that I haven't found A N Y  explanation that uses real-world numbers on even a simplified model to explain the source of the 10,000 N required to support a 1-tonne light aircraft in level flight.

@BlastWave Perhaps you are looking in the wrong place.  I suggest you look in any undergraduate aerodynamics textbook.  I am also curious what your definition of "explanation" is.  What would satisfy you?  There are no analytical solutions for 3D lifting flow -- this means we must use numerical methods to solve any 3D lifting flow.  Here is a link to Bertin & Smith, check out Example 7.2 that starts on page 365.  https://www.airloads.net/Downloads/Textbooks/Aerodynamics-for-engineers-%20John%20J.Bertin.pdf

The end result of that example is Figure 7.32, which gives the lift coefficient vs. angle of attack for the given wing.  You can easily dimensionalize that lift coefficient at a wing area and flight condition (airspeed and altitude) of your choice to see the magnitude of force that is created.

Big issue with Bertin's book (Chapter 7). Air, a gas, is treated as incompressible. Physics basics say there are 3 states: solid, liquid, gas. Bertin claims only solid or fluid. He also seems to misunderstand the key differences between liquids and gases, established in 17th century! Liquids have weaker bonds than solids, and gases have none. This directly affects how they fill containers (gas expands, liquid doesn't). Basically, the book ignores key properties of gas.

A quantity of gas will fill a container of any volume. A quantity liquid will retain its volume irrespective of the volume of its container.

@BlastWave That is not at all what incompressible means in the aerodynamic sense.  Not even in the slightest.  When we say that an aerodynamics problem is incompressible, we are saying that the density is constant throughout the problem of interest.  It can be whatever it needs to be (expand to fill the container), but whatever that value is, it is going to be a constant for our system.

Further, aerodynamicists do not always treat air as incompressible -- instead, we recognize that in certain limited circumstances, we can treat air as incompressible.  This is not a property of air, but instead a property of the circumstances.

Take a bar of metal.  If  you throw it, you can likely treat it as a rigid body.  If you constrain one end and apply a moderate load, you can likely treat it as a linear elastic structure.  If you apply a heavy load, then it will deform in a nonlinear, plastic manner.  Rigid, elastic, or plastic is not an attribute of the bar.  It is an attribute of the circumstances and the bar.

Let us continue this discussion in chat.

Are you seriously suggesting that "incompressible" has a meaning in aerodynamics different to that in classical physics? Or that the density (mass per unit volume) of a quantity of gas (air) change other than by changing its volume? Is there nobody out there who doesn't see the paradox in that idea?

My 6th edition Bertin (vs. your 5th) expands on fluid as a continuum (section 1.2.2) but gets tangled. It claims a "continuous flux...through boundaries" while maintaining a "constant number of molecules." This is illogical. Continuous flux means uninterrupted flow, while a boundary implies limitation. This wouldn't work for gases: they expand to fill their container, and without a defined volume (no container), gas volume is meaningless


text:
Is it possible to order or purchase a hardcopy of an NTSB report?
I am an independent researcher working closely with several NTSB aviation accident reports and would prefer a printed hard-copy. I realize I can print out all of the relevant sections of each report but was curious as to whether hard-copies are published by NTSB?
*Edit: I am working on a museum display which would include the presentation of a hard-copy of a report. The specific packaging by NTSB would be valuable to me in this context.

Contact the NTSB...

You can get them from sellers on Amazon book-on-demand. Which reports do you need? Give me a day to upload them to Amazon book-on-demand... ;) ;)  J/K take the PDF on a USB stick down to Kinkos or other competent copy shop, and they'll print it out and bind it for you.

I'm not sure that this is on topic, but the short answer seems to be that you need to contact the National Technical Information Service. NTSB reports used to include this text:

Accident reports, safety studies, special investigation reports,
statistical reviews, and safety recommendations may be downloaded from
the NTSB Web site, or printed copies may be purchased from:
National Technical Information Service
5285 Port Royal Road   Springfield, Virginia 22161
(703) 487-4630 (Subscription Orders)   (703) 487-4650 (Single-Copy
Orders)
(Subscription rates apply to certain recurring publications)

The current wording is:

Copies of NTSB publications may be downloaded at no cost from the
National Technical Information Service, at the National Technical
Reports Library search page, using product number PB2020-101001. For
additional assistance, contact—
National Technical Information Service
5301 Shawnee Rd.
Alexandria, VA 22312
(800) 553-6847 or (703) 605-6000

Alternatively, since NTSB reports are in the public domain (with some limited caveats) you could just get them printed at your local print store, presumably much more quickly and cheaply than by going to NTIS.

Are you looking for the big ones with titles with "NTSB/AAR[yr]-[number]" in them (as opposed to the shorter, automatically-generated reports you get by browsing around in the NTSB's aviation accident database?
If so, most of them can be downloaded in PDF format from the NTSB website, free of charge, although some of the reports listed (especially the older ones) don't have an online copy available there.  Alternatively, Embry-Riddle Aeronautical University's Hunt Library holds their own copies of every NTSB/AAR[yr]-[number]-series report that has been published, and has PDFs available on their website for every single one, also gratis.

The Embry-Riddle connection is valuable, but it sounds like the questioner already knows how to download PDFs.  For whatever reason, the question is about something else.


text:
Will control surfaces on a plane be less efficient at a higher altitude?
I may be wrong but I learned that control surfaces depends on the air flow to work properly, and that airliners have a higher cruise altitude because of the less dense atmosphere, improving the fuel efficiency.
But that got me thinking:

Will control surfaces on a plane be less effective at a higher altitude because of the less dense air?
Do modern airliners have a workaround to solve this problem?

Please let me assume that you wonder about control surface effectiveness rather than their efficiency. Both are closely related, but I prefer to address their effectiveness - doing what the pilot demands them to do.
The aerodynamic forces are proportional to the dynamic pressure $q$ of the flow, which is density times velocity squared, as in
$$q = \frac{\rho}{2}\cdot v^2$$
To create the same amount of lift at a higher altitude, the airplane has to fly faster, so in effect the forces can stay the same. Only the true air speed will be different, which helps to get where you want faster. The control surface effectivity remains unchanged.
If we dig a little deeper, the atmosphere cools down with increasing altitude until you reach the Tropopause. This cooling makes the engines more efficient but also reduces the Reynolds number of the flow around the aircraft. A lower Reynolds number translates into a thicker boundary layer, which will reduce the effectiveness of control surfaces a tiny bit and will reduce the range of their best effectivity. But this effect is so small that it has no practical consequence.
Airliners fly at transsonic speeds at altitude, so now sonic effects become more pronounced. For the control surfaces this means that they will lose their effectiveness at higher deflection angles. For small corrections all is very similar to low level, slow flight, but if you need full deflections the control surfaces are indeed less effective at altitude.
Another effect will be rather more pronounced, and this is aerodynamic damping. Damping is the tendency of a system to create additional forces from movements which run against this movement. Take a wing: If the aircraft rolls, the wingtips will move up on one side and down on the other. Both movements will add a small angle of attack, lowering the total angle of attack on the up moving tip and increasing it on the down moving tip. Both tips will see a change in lift which will counteract the rolling motion. If the rolling speed is $\omega_x$, the resulting change in angle of attack $\alpha$ at a wing station $y$ is
$$\Delta\alpha = arctan \left(\frac{\omega_x \cdot y}{v}\right)$$
As you can see, the flight speed is in the denominator, so a higher flight speed will create a smaller angle change for the same roll rate. The same holds true for the other axes of movement, and in consequence the higher-flying aircraft needs either more pilot attention or an artificial damper.
I guess it is the lower damping which made you think that the control surfaces are less effective. They aren't.

@jedd.ahyoung: Yes. And when going faster some things do change subtly, so altitude does make a difference.

I'm glad we've got guys on here like Peter who really know the science to set us straight!

Control effectiveness is dependent on airflow. Flying slower or through thinner air makes the controls less effective. However, given the same indicated airspeed (IAS), the same number air molecules are passing by the control surfaces, so the effectiveness will be the same. Do note that a given IAS results in higher true airspeed (TAS) in thinner air (higher altitude).


text:
How much thrust can the thrust reversers create?
Let's say for the sake of the question, the plane is an 787 Dreamliner and the engine is the General Electric GEnx-1B64 (that according to Wikipedia can produce a maximum thrust of 284 kN)

In comparison to the "regular forward" thrust that a jet engine can generate, how much thrust can we apply to this engine in the reverse mode?
Can we apply full power in the reverse mode?

You're question is not clear.  Full power can be applied with the buckets deployed but is your question "what is the effective thrust"?

@Simon, now I haven't flown the B787, but I'm quite sure that the full rated N1 can not be applied with reversers deployed, more likely "full reverse thrust" is a lower N1. Gabriel, once again not sure about B787, but on most (if not all) Boeings the reverse thrust levers locks the forward thrust levers electro/mechanically from moving out of idle thrust, so you instead control N1 with the thrust reverse levers. On the B737 you usually don't see more than ~84,4% N1 with max reverse thrust, with max rated N1 usually being around ~100% (someone with better manuals might have more exact numbers)

(I should probably add that the numbers I'm mentioning above are for the CFM56-7B27)

@Waked plz write this in the answer.

@GabrielBrito Sorry Gabriel, but I am not certain enough about other aircraft types to provide a generalized answer. This discussion might be of interest to you: http://www.airliners.net/aviation-forums/tech_ops/read.main/316228/ (Just be careful not to confuse N1% as % of rated thrust, as the relationship is non-linear, not mentioning inefficiencies from the flow mechanics being different for reverse and forward thrust).

@Waked although your knowledge lies with 737, your information is worth more than a comment. I support you to convert comment to proper answer.

Estimations
We can at least estimate a reverse thrust case based on some numbers and some physics, a bit of a specific case of this question. The stopping distance equation:
$$d_f=\frac{v_i^2}{2a}$$
The information in Appendix B here for the 727-200 gives stopping distances for different cases. If we look at a sea level pressure altitude case with 120,000 lb gross weight, the stopping distance is 2452 feet. The correction for a reversers only case is 2.57, bringing the distance to 6302.
At a landing speed of 200 ft/s, the plane will take 11500 lb of force to stop in that distance. Each engine on the 727-200 provides 14500 lb of thrust force maximum. Considering that part of the stopping force will be provided by drag and surface friction, the reverse thrust is about 25% of the maximum forward thrust. The reversers will be more effective at higher air speeds, so the maximum will be higher than this.
Figure 39.5 here shows a graph of reverse thrust compared to forward thrust for different bypass ratios and reverse thrust types. This is a good check for a general case. The GEnx-1B64 has a bypass ratio of about 10, and reverses the fan but not the primary exhaust, which gives a ratio of 30% of maximum forward thrust.
Summary
The engine will not run at full power when in reverse mode, so accounting for this and the bypass ratio will leave you with about states that modern thrust reversers can convert up to 35% to 50% of their forward thrust into reverse thrust.


text:
How can I find out what time an airport was closed due to weather?
Where do I find at what time an airport was closed, due to inclement weather, on a specific date? I completed the first leg of my flight, which was one hour from take-off to landing. When I arrived in my connecting city, my final destination airport was closed due to weather conditions. Why did they not cancel my entire flight before I departed on the initial leg of the flight?

I would expec that the flight took off for your connecting city because there were people on the plane whose destination was that city.  Are you asking why the airline didn't notify just the passengers who were continuing to the closed airport?

Yes, my destination was a small mid-western airport. More than likely, my family of three were the only passengers continuing on to my destination city.

The best way to get that information would be to call Airfield Operations at the airport in question.  They can tell you what time the airfield was closed, IF it was the airport itself that was "closed" in that situation.  Oftentimes, however, the field itself isn't technically closed, but the weather was simply so bad that nobody was getting in, and that gets discussed as "the airport is closed" due to weather.  Not technically accurate, but close enough for discussions of "can flights get in there or not."
As for what happened before you left for your connecting city, all sorts of answers are possible.  Perhaps the weather wasn't that bad initially, and it looked like your connecting flight had a good chance of going.  Or perhaps "the system" slipped up, and they should have notified you that the connecting city was as far as you'd be likely to get, and they didn't.  Or perhaps there were PA messages made to that effect that you didn't hear. (It happens.)
Also, an airline wouldn't cancel the flight to the connecting city, since some passengers presumably were trying to get there as their destination, and others had other connections to make to cities that weren't affected.  What could happen if they knew early enough that your second flight wasn't going to go, and recognized soon enough that "this passenger won't get where they're going today", is they'd advise you of the situation, and offer you the option to cancel your trip, rebook the next day, or get to the connecting city so you're that much closer when the weather has passed & flights resume.  Depending on multiple factors, any of those might be a reasonable choice for a passenger to take, so they offer the options, rather than unilaterally cancelling your ticket.
It's also possible that the airport itself made some sort of call that "we're closed" at some point after your first flight had taken off, surprising the dispatchers at the airline.  In that case, you are, plain & simply, out of luck.  Not desirable, but in the millions & millions of airline flights and hundreds of millions of passengers flying every year, it sometimes happens.
Reviewing the weather reports for that timeframe from someplace like Weather Underground might shed light on just how bad the weather was, and when the forecasts were amended.  Making sense of that would require some familiarity with aviation weather reporting formats, though.

Thank you for your response. Just to clarify, I didn't expect the airlines to cancel any flight in total, just cancel me and my family (and what few other people who may have been headed to my small mid-western airport. The ice and snow had started coming down by mid-night. We were surprised that the flights were not canceled initially. Unfortunately, we were headed to my mother's funeral and were hoping for the best).


text:
How does the FAA determine which format of location identifier to assign to an airport?
In the U.S., FAA location identifiers are assigned to registered aerodromes. However, these can have different formats:

3 Letters (e.g. ORD)
1 Number and 2 Letters (e.g. 1AD)
2 Numbers and 1 Letter (e.g. 25M, 8M1, or M72)
2 Letters and 2 Numbers (e.g. TN01, 1CA3, or 50SD)

How does the FAA determine which of these formats should be used when assigning the identifier for an airport?

In short, the scheme is as follows:

Busier airports get 3-letter identifiers.
Less busy public-use airports usually get 2 numbers and a letter, sometimes 1 number and 2 letters.
Less busy private airports (which is almost all private airports) get 2 letters and 2 numbers.

More specifically, the FAA assigns airport identifiers (and location identifiers in general) according to the guidance laid out in section 1-2-7 of JO 7350.9.
3 Letter Identifiers
For airports, 3-letter identifiers are assigned to airports that meet the following criteria:

Airports:
(a) with a manned air traffic control facility.
(b) with a navigational aid (NAVAID) within airport boundaries.
(c) that receive scheduled route air carriers.
(d) that receive military airlift services.
(e) designated by the U.S. Customs Service as Airports of Entry.

or

Public use airports commissioning Automated Weather Observations Systems, level III (AWOS-III) or higher that have paved runways 5,000 feet or longer.

1 Number, 2 Letter Identifiers

Most one−number, two−letter identifiers have been assigned to aviation weather reporting and observation stations and special−use locations. Some of these identifiers may be assigned to public−use landing facilities within the United States and its jurisdictions, which do not meet the requirements for identifiers in the three−letter series.

The format of these codes is as follows:

In this identifier series, the number is always in the first position
of the three−character combination.

For example, 1AD would be a valid code.
2 Number, 1 Letter Identifiers

Most one−letter, two−number identifiers are assigned to public−use landing facilities within the United States and its jurisdictions, which do not meet
the requirements for identifiers in the three−letter series.

The format of these codes is as follows:

One−letter, two−number identifiers are keyed by the alphabetical letter. The letter may appear in the first, middle or last position in the combination of
three characters.

For example, 25M, 8M1, or M72 are all valid codes.
2 Number, 2 Letter Identifiers

Two−letter, two−number identifiers are assigned to private−use landing facilities in the United States and its jurisdictions which do not meet the requirements for three−character assignments.

The format of these codes is as follows:

They are keyed by the two−letter Post Office or supplemental abbreviation (listed below) of the state with which they are associated. The two−letter code
appears in the first two, middle, or last two positions of the four−character code.

For example, TN01, 1CA3, or 50SD would be valid codes.
The order continues to list a table of supplemental codes that can be used instead of the state's mail code. This allows for states whose mailing codes wouldn't work well as part of the identifier and also for states which need more than the 300 private airport registration codes possible with a given 2-letter sequence in this format.
Changes to Existing Identifiers
Airport identifiers are preferred to keep the same code once it's assigned, except in exceptional circumstances. According to section 1-2-4 of the same document:

Location identifiers are considered permanent and will not be changed without strong and documented justification, primarily concerning air safety or a significant change of landing facility status.

As a result of this, it's possible for an airport which now meets the qualifications for a 3-letter identifier to still have an identifier containing numbers due to it not having met the requirements for three letters when it was assigned. 8A3, Livingston Municipal Airport is an example of this. It has an AWOS-III and a paved runway longer than 5,000 feet, but still retains the code 8A3, which was assigned before the runway was lengthened.

Regarding identifiers being permanent, the same holds true for 3-letter identifiers that no longer meet the criteria. For example ACQ qualified for that code because of the NDB that was located on the field until recently. Now the airport no longer meets any of the criteria for a 3 letter identifier but ACQ is permanent.


text:
Why are the letters "I", " N", and "O" omitted from the SELCAL pool?
Why are the letters "I", " N", and "O" omitted from the SELCAL pool?

Related (presumably) https://aviation.stackexchange.com/questions/66845/why-are-oscar-india-and-x-ray-o-i-and-x-not-used-as-taxiway-identifiers/

Perhaps N looks a bit like H?

From the ASRI SELCAL Users Guide:

The four tones required for a single SELCAL code assignment are selected from a
total of sixteen tones available in the ground station SELCAL installation. For
convenient reference, the sixteen tones are designated by letters of the alphabet
(“A” through “S”; with “I”, “N”, and “O” omitted). Tones “P”, “Q”, “R”, and “S”
were the four tones that were added to the exiting 12 tones in 1985.

Although this specification states that N is not used, it does not say why. However, there may be a clue in that the first implementation used 12 letters, A through M (omitting I). When four more codes were added in 1985, they presumably wanted to omit O for the same reason they omitted I (confusion with digits 0 and 1). If they continued in the same sequence then the "new" codes would be N, P, Q, R. Knowing that they were going to have to skip O, it may have been seen as simpler at the time to introduce the four new codes in contiguous sequence: P, Q, R, S.
The linked copy of the document above does not mention SELCAL32, which has been approved for implementation in November 2022. SELCAL32 uses a set of 32 codes, 16 from the previous SELCAL plus T through Z and 1 through 9. Again note that 0 is omitted. More information can be found at the ASRI SELCAL Registrar Services page.


text:
Why does the Tu-22M3 nose have this peculiar shape?
What is the reason behind this unusual nose shape? I am not referring only to the presence of the protuberance on the tip, but mainly to the asymmetry between the top and bottom side.

Image source
It can be seen better in the profile depiction here:

Image source

The F-111 has a very similar nose shape. Possibly related?

To make it look more badass?

Nobody knows why except Andrei Nikolayevich Tupolev, and he is dead.
Andrei Tupolev was known to insist on the fast and adequate at the expense of the theoretically correct, leading to widespread technical debt in his designs. He may have raised the nose cone for no more profound reason than to get the refueling probe in line with the pilot's vision. Once he had energetically dictated where the probe was to go, no one at the design bureau would dare suggest moving it; they would just work the forward avionics into the resulting odd shape as best they could.
Tupolev died in 1972 leaving this and many other of his decisions unexplained.

"Andrei Tupolev... leading to widespread technical debt in his designs." Interesting. What other unexplained design curiosities did he leave behind?

technical debt seems to imply that it caused problems later... is that the case?

The Tu-22M3's nose houses a Leninets PN-AD radar and a NK-45 navigation and attack system. The NK-45 provides improved low-altitude flight, compared to earlier models.
Several Tu-22M3's were converted to Tu-22M3R who carry a Shompol side looking airborne radar and other Electronic signals intelligence equipment.
All this equipement is stored in the nose of the aircraft. This explains the strange appearance (The asymmetry between the top and bottom).
*Edit:
I can only guess why the nose is asymmetric: Maybe some parts of the equipment located in the nose has to lock forward / down of the plane. The asymmetric bottom may provide a better "view" for the equipment. (See my comment below).
On this image, you can see all the equipment in the nose. Unfortunately the quality is too poor to be able to read the caption.

Image source
The Tu-22M had a retractable probe on the top for aerial refueling:

As a result of the salt negotations, the probe was removed but it could be reinstalled.

because with refueling it was considered an intercontinental range strategic bomber.

Janes-All-Worlds-Aircraft-1980-81
and

the Soviets secretly agreed to reduce Tu-22M production to thirty aircraft per year and not to give them an intercontinental range.

Stratetic Arms Limitation Talks 2
Overall Source

This does not appear to answer the question.

@JonathanWalters Can you explain why?

You have some great info about probes and equipment, but the question is regarding the asymmetrical nose, "the asymmetry between the top and bottom side"(see the second sentence in the question). You do give the one statement: "This explains the strange appearance" which may or may not refer to the asymmetry. If it does, then this should be emphasised and expanded upon; if it does not, you have not addressed the main thrust of the question.

Well, I can only guess, but it seems like some electronic equipment in the nose has "to look down and forward" of the plane. Therefore, the nose is shaped the way it is, to enable a better "view" for the equipment. However, I don't find any reliable information about this, that's why I didn't include it into the answer.

Sorry for further complicating things, but it seems to me this nose section will produce some lift. Could it be possible that somewhere in the design process there was a need for moving the center of lift slightly forward?


text:
Aircraft pilot's seats: what is the notch for?
If you do a Google or Bing search for "Aircraft Pilot Seat" then choose images, you might notice a large number, perhaps majority of them, have a notch cut out of the front of the seat. What is this notch for?
Notches are circled here:

Original Source
(Please, no potty humor or scatological jokers need apply here)

It's either for clearance of the column of the yoke or moving the crotch strap of the harness closer to the body of the pilot.
Alternative yoke designs remove the need for the notch:

(source: airliners.net)
Alternative control methods like the Airbus sidestick also remove the need. As Henning Makholm noted, the seat strap just goes through the cushion.

+1 If you google for pictures of A320/A330/A380 flight decks, which have sidesticks instead of yokes, many of them show clearly the pilot's seats there do not have the notch. Instead the crotch strap is just fastened in the middle of the seat cushion.

It's for the control column when it is moved fully aft.
Example:

Source
If you only needed a crotch strap, it can be installed mid-seat.

Pilot seats have a five point harness with a crutch strap.  The strap needs to be snug to provide any value in a sudden stop, hence the 'notch' to bring it as close to the body as possible.


text:
What are the risks in landing on a beach vs. shallow waters?
I recently read a story where a pilot of a light aircraft died having attempted to land on a beach.
Would it be potentially safer to try an emergency landing on a beach, or go for shallow waters of 6-10 feet depth, or deeper water? (In the absence of anything more suitable).

Re-read that story, if it was the recent crash in Florida.  The pilot didn't die, the person he struck on the beach while landing died (and the other person he hit was left in critical condition).

6-10 feet is more than draft of even large aircraft before it takes on water and is therefore deep for all practical purposes. Including evacuation as it's more than shoulder height and you'd still have to swim.

I would just like to add that while pilots are using this as a guideline it doesn't take into account that the beach may be full of people. Yes, it's safer for the pilot to land on dry land, but if the beach is completely filled up, people will die, like they did on 2nd of August in Portugal. Pilot chose the beach, landed safely, two people died including an eight year old child.

I'm here because of the "Dunkirk" beach landing scene

Having done my primary training essentially over beaches I'm pretty well-versed in the theory (but thankfully not the practice) of landing on beaches.
Given the possible choices offered at your typical beach, the order of preference for landing areas is generally:

Pavement
People like to drive their cars to the beach. There's probably a road or parking lot nearby, and if it's empty enough that's where you want to land.
Dirt (not sand)
Some beaches have "sandy dirt" areas, usually with low grasses and the like on them. If the beach you're contemplating has such an area it's probably your second-best choice as it will be the firmest ground and closest to landing on a grass strip. (Beware of bumps and rocks!)
Wet Sand
The sand between the high-water mark and the low-water mark on the beach tends to be fairly compacted, so it can make a decent landing area. It will probably be softer than dirt/grass, but give it your best soft-field technique and you can probably set the plane down without damaging it.
Properly executed you can put the plane down without doing any substantial damage, and if it's an actual emergency you're unlikely to get in any trouble.

Dry Sand
Fluffy dry sand is a decidedly soft field situation - soft enough that in a nosewheel aircraft there's a very good chance that no matter how careful you are or how good your soft-field technique is you'll lose one or more of your landing gear - but at least you're on dry land.
The recent incident in Florida is an example of this: the aircraft's nose gear was sheared off as you can see below, but the pilot and passenger walked away (sadly some bystanders on the ground were injured, and one was killed).

Water
Unless your plane is on floats water is basically the landing of last resort - particularly for fixed-gear aircraft. The forces involved in putting your wheels into even 6-10 inches of water are pretty substantial, and there is a real chance of tearing off the gear or losing control of the aircraft in the last few seconds.
Even if the actual landing is uneventful you will be left to contend with being in the water while evacuating the aircraft which adds complexity to an already difficult situation (and if you're far enough out that the depth of the water is measured in feet you're going to have to swim back to shore once everyone is out of the aircraft).

"Ditching" an aircraft in the water is a subject worth looking into on its own. Smarter people than I have written and spoken volumes about it, but as Skip Miller pointed out we don't really have a lot of hard data.

As a related aside, once the aircraft is on the ground and everyone is safe you should give some thought to securing the aircraft, both to protect the plane and to protect the environment. If on the beach pull the aircraft above the high-water mark so that the rising tide won't soak the landing gear/fuselage in salt water, and to prevent fuel/oil/etc. from being washed off into the water. Obviously this is a much lower priority than seeing to people/passengers' safety, but it bears remembering once the more important stuff is attended to.

if you are really good you can use the water to slow down and then actually stop on the sand

It may be worth pointing out that Copalis State Airport (S16, in Washington State), is a beach, and an official runway... the sand is hard packed enough to be a runway for both landing and taking off for most light airplanes.

we don't really have a lot of hard data.  Roger that. After a Columbian C-130 ditched the USAF updated the flight manual drawing of a ditched 130 along w/ some notes & minor procedural changes. So even after 25ish years of operation Lockheed & the AF didn't know what to expect. Fun Fact: One of the fatalities was the navigator, shot by the pilot as the plane glided, out of fuel.

@ratchetfreak yeah! http://www.crazedpilot.com/big-rocks-long-props-volume-5-high-country/

This question is incomplete without a mention of the Traigh Mhor airport on Barra, which shows that for the right aircraft, on the right sort of beach, at the right state of tide, the probability of a successful landing is good enough to sustain a commercial service.

And previously from a major airline... (though operated by Loganair in both cases)

There were some doubts about the sustainability of this service as the Twin Otters approached retirement age, but they are now back in production, probably thanks to this and similar niche roles.
(Picture source)
Second picture source

Keunyeonpyeong-do has a beach like this, The sand over there is incredibly compact and thus allow airplanes to land on it.

mind that these aircraft have pretty rugged landing gear and low pressure tyres in order to make landing on those beaches regularly a good idea. For your average Cessna or Piper I'd not recommend it.

No difference between "deep" or the 6' - 10' depths you propose.
As far as landing on the beach, there just are not enough incidents of this happening for anyone to give you a good statistical analysis of actual accidents from which to draw a conclusion.  There are too many variables.  One example: some beaches you can drive a car on, other beaches are so soft the wheels are likely to dig in and cause an abrupt stop or a flip.

In a light plane, you definitely want to avoid water unless you are on a plane with floats.  If the wheels are down the when you touchdown in the water there is a high probability of wheels digging in and the plane flipping over nose first.  This type of accident is often not survivable, broken necks, etc.  When I learned to fly amphibians one of the first things you were taught was to verbally repeat "land on land, gear down;  land on water, gear up" before every landing.
Landing on smooth damp sand can be like landing on pavement.  You land normally and just ensure you keep you momentum up until you get to your parking spot.  This type of beach landing is pretty common in Mexico.  The hardest part is usually the taxing because you leave the damp sand and end up going into soft dry sand which requires power which throws up sand that abrades the paint on your plane.

Barry Schiff's piece on ditching seems to refute the fixed-gear-planes-will-nose-over rumors; they're addressed in several other places as well. While I certainly wouldn't make water my first choice, a properly-executed (nose-high) water landing in a tricycle fixed-gear aircraft shouldn't be ruled out just because "the plane might flip" -- indeed you might just as easily flip the plane if the nosewheel digs into soft sand.

There is no guarantee the plane will nose over, but there is a higher probability.  Having landing several times on wet sand I would select it every time over water in an engine out. Wet sand is pretty darn hard.  My last plane weight around 6,000 pounds and we never had any trouble landing on wet sand.  There are even some Youtube videos of pilots landing transports on the beach, https://www.youtube.com/watch?v=Vat0h18SeHs.  Here is what happens if you forget to retract on an amphib, https://www.youtube.com/watch?v=56IoiW8n5mc.  But the final decision is up to the PIC.

My issue isn't with your choice of procedure (I would make the same choice as you), it's with your "high probability" statement. To say that there is a "high probability" that ditching a fixed-gear aircraft (or a retract with the gear down) will result in a nose-over seems to run counter to the (limited) evidence/date I've turned up for GA ditchings.  If you have actual quantitative data supporting that I'd be very interested in it - everything I've read acknowledges that it's a risk (same as landing on soft sand), but a vastly overstated risk.


text:
What is the difference between a crabbed and de-crab landing?
Both landings are done when an airplane's nose is not in inline with the runway. How are these two different? when should one technique be preferred over other?

Consider where the center of gravity is in relation to the main wheels. If you are in a tail dragger, you definitely would prefer to de-crab (never heard that term before now) before touching down. If you touched down while crabbed, you'd have a moment created by the center of gravity around the main gear to ground loop the airplane.
In a tricycle gear airplane, that same moment would work to straighten the airplane since the center of gravity is forward of the main gear.
In a crosswind from the right, for example, when you apply left rudder to align the aircraft with the runway, the right wing will want to come up (you just gave it a little extra speed), so you will want to use right aileron to at least counter that as you certainly don't want the crosswind component to get 'under' the wing.
Both 747 operators I flew for recommended touching down in the crab. Personally I didn't like that and used a combination approach in a heavy crosswind, take out some of the crab but not all. Also, while they did caution against lowering the upwind wing, I always lowered the wing a little. I once figured out how much the wing would have to be lowered before ground contact, and it was quite substantial, more than I would ever think of using. Also, as I remember, It would not be the wingtip or an outboard engine pod that would make first contact, but rather the outboard corner of the outboard wing flap when set to flaps 30.
Finally, when your touch down speed is 140 knots, for example, you'll have to crab much less for a given crosswind component than if your touchdown speed is 70 knots. Cosine or tangent of the angle, I forget which.

crosswind/ground-speed=tangent of crab angle

"the outboard corner of the outboard wing flap" - even so, do they take it out of your paycheck?

@davidbak The first 747 carrier I flew for was non-unionized. They simply fired pilots who screwed up (or for that matter just caused too much discontent in management's eyes). The second was unionized. My guess is that a captain scraping a wing would have been demoted to f.o. for awhile. Nobody ever did such while I was flying for them, so it really wasn't an issue.

Wikipedia's definitions are a bit unclear but it seems to say that de-crabbing is where you straighten the aircraft in the air just before touchdown; crabbing is where you straighten on the runway after touchdown.
De-crabbing:

Just before the flare, opposite rudder (downwind rudder) is applied
  to eliminate the crab

Crabbing:

upon touchdown the airplane tracks towards the upwind edge of the
  runway while de-crabbing to align with the runway. Immediate upwind
  aileron is needed to ensure the wings remain level while rudder is
  needed to track center line. The greater the amount of crab at
  touchdown, the larger the lateral deviation from the point of
  touchdown.

Personally I find these definitions odd: in my limited experience in light aircraft, a "crabbing" approach is what Wikipedia calls "de-crabbing", and "de-crabbing" is the action of straightening the aircraft in the air before touchdown. I have no idea why a pilot would prefer to land the aircraft at an angle to the runway and then correct on the ground. But perhaps this is normal practice in larger aircraft; I have no idea about that.

Some larger aircraft prefer to land in the crab and correct after touchdown.  The reason for this (as far as I can tell) is to avoid the possibility of an engine or wing strikes when correcting for drift after un-crabbing.

You interpreted it correctly.  :)

It also depends if you have a low or high wing airplane.  And if you are comfortable touching down on one wheel.
In my plane, A Socata TB, the plane has a monstrous rudder that has a demonstrated crosswind component of 25 knots.  That's demonstrated, I'll tell you it has the authority to do more but the manufacturer always errs on the side of safety.  It also is a low wing, so high crosswind landings get be nervous that I might scrape a wing edge.
To me being sideways is not normal.  Crabbing to the runway means that you are heading at the runway but it may not be at your nose.  But it is holding a steady view relative to a point on your windscreen.  Remember, the training if you see another plane.  If it's moving relative to a point on your windshield that's good.  If it's not and maintaining the same point, you are generally on a collision course.  Same with the runway numbers, if they are off to your left and the runway is coming at you, you might be pointing at the control tower but your "Ground Path" is straight down the runway.
I'll crab all the way down, then bleed off energy using the T-6 P-51 training I received, then just as I feel the final drop beginning, I'll add about 2 inches of MP to arrest the decent and kick out to point the nose down the runway.
Remember, the only time your wheels have to be straight down the runway is 1 millisecond before the rubber hits the road!
Also in retrospect, I assume the turn Crabbing is derived from the way a real Crab moves.  It walks sideways to go forward.

the "demonstrated cross-wind" has to do with the way FAR certification is worded, and has nothing to do with erring on the side of safety, eg: `§25.237 - Wind velocities.
(a) For land planes and amphibians, the following applies:
(1) A 90-degree cross component of wind velocity, demonstrated to be safe for takeoff and landing, must be established for dry runways and must be at least 20 knots or 0.2 VSR0, whichever is greater, except that it need not exceed 25 knots.`

Agreed, it 'need' not exceed.  But that does not mean that it can't exceed or planes would be consistently under-engineered.

It all depends on the aircraft you are flying.  Some jetliners are certified to be landed with side loadings if that side loading on landing is within certain limits.  Some airliners like the 737 require the jet to be landed in a crab as cross controlling to keep the nose aligned with the runway centerline runs the risk of scraping and damaging one of the engine nacelles on the runway.
Light GA aircraft are not designed to take high side loads on their landing gear and require cross control to align the jet with runway centerline during crosswind landings.  In an airplane fitted with conventional landing gear (tailwheel), it is imperative to land parallel to centerline with good crosswind technique as side loading creates a strong possibility on inciting a ground loop.


text:
High performance endorsement in airplane modified by STC
I had trained for my complex and high-performance endorsements in an airplane that was certified with an engine that does not meet high-performance criteria but had been modified by STC such that it did meet criteria.
The logbook endorsement mentions the model of the airplane and that it had been modified such that the aircraft produced more than 200 horsepower. The question is do I need to actually track down the STC information just in case of a ramp check or when going for a more advanced pilot certificate?
Edit:
This question was posted due to a conversation with a flight instructor who had balked at the legality of the endorsement. His argument essentially went like this:
1) If you have an aircraft with a "200 HP" factory new engine, you put it on a dyno, it generates 205 HP. It's still a "200 HP" engine as per the FAA.
2) If you have an aircraft with a "200 HP" engine, you do a top-of-the-line overhaul, you put it on a dyno, it generates 205 HP. It's still a "200 HP" engine as per the FAA.
3) If you have an aircraft with a "200 HP" engine, you apply an STC that changes the cylinder and piston configuration to intentionally generate 205 HP, you put it on a dyno and it does make 205 HP, now because the intent of the STC being to generate more than 200 HP and the FAA approval via STC as a "more than 200 HP" engine the aircraft only at this point meets the high-performance criteria.
His argument was that in cases 1 and 2, since the engine was not "modified" with the specific intent to generate more than 200 HP you merely won the horsepower lottery but it's still certified as a 200 HP engine. He had questioned whether the STC was intended to bring the power output above 200 HP or if it was just an accidental byproduct and it was still therefore certified as a 200 HP engine.

You shouldn't, the CFI's signature and that note should be enough.

CFIs are only people and often wrong.

The FAA only requires that you have training in the high performance aircraft as per FAR 61.31:

(f)Additional training required for operating high-performance airplanes.
(1) Except as provided in paragraph (f)(2) of this section, no person may act as pilot in command of a high-performance airplane (an airplane with an engine of more than 200 horsepower), unless the person has -
    (i) Received and logged ground and flight training from an authorized instructor in a high-performance airplane, or in a flight simulator or flight training device that is representative of a high-performance airplane, and has been found proficient in the operation and systems of the airplane; and
    (ii) Received a one-time endorsement in the pilot's logbook from an authorized instructor who certifies the person is proficient to operate a high-performance airplane.
(2) The training and endorsement required by paragraph (f)(1) of this section is not required if the person has logged flight time as pilot in command of a high-performance airplane, or in a flight simulator or flight training device that is representative of a high-performance airplane prior to August 4, 1997.

(By the way, notice (2) above, you don't even need an endorsement if you logged any time as PIC in a high-performance aircraft, flight sim, or FTD prior to 8/4/97!!!)
So going over what your CFI said:

1) If you have an aircraft with a "200 HP" factory new engine, you put it on a dyno, it generates 205 HP. It's still a "200 HP" engine as per the FAA.
2) If you have an aircraft with a "200 HP" engine, you do a top-of-the-line overhaul, you put it on a dyno, it generates 205 HP. It's still a "200 HP" engine as per the FAA.
3) If you have an aircraft with a "200 HP" engine, you apply an STC that changes the cylinder and piston configuration to intentionally generate 205 HP, you put it on a dyno and it does make 205 HP, now because the intent of the STC being to generate more than 200 HP and the FAA approval via STC as a "more than 200 HP" engine the aircraft only at this point meets the high-performance criteria.

1: It is still a >200HP aircraft
2: It is still a >200HP aircraft
3: It is still a >200HP aircraft
STC's aren't just some paperwork the manufacturer creates for aircraft modifications, they are approved by the FAA, side-effects and all, for installation on specific airframes.
You could counter your CFI about that... Ask him if flying an aircraft that had a STC bringing it into the >200HP still requires a high-performance rating. Of course it does! Now why can't you get your high-performance rating in that aircraft? You can! If you flew that aircraft without the rating and you were ramp checked, you would be violated. The FAA doesn't care if the aircraft has >200HP as it was factory built, or if it was modified by STC to get there.

No.  All that’s required is that you received ground and flight instruction in an aircraft which meets the requirements for a high performance airplane in 14 CFR §§61.31 (f) and received an high performance endorsement from an authorized instructor in their logbook.  If the approved STC makes alteration to the engine such that the power out is now rated to exceed 200 bhp per the terms of the STC, then the airplane would be considered high performance under §§61.31.


text:
How do witness marks on propeller blades provide data on estimated blade angles at the time of impact?
In the NTSB Powerplant Group Chairman Factual Report for the 2014 crash of the King Air B200 in Wichita Kansas (NTSB# CEN15FA034), I read:

"Neither propeller was feathered before impact. Both engines exhibited
multiple internal damage signatures consistent with engine operation
at impact. Engine performance calculations using the preimpact
propeller blade angles (derived from witness marks on the preload
plates) and sound spectrum analysis revealed that the left engine was
likely producing low to moderate power and that the right engine was
likely producing moderate to high power when the airplane struck the
building."

What are witness marks on a propeller blade? And how do they provide data on estimated propeller blade angles at the time of impact?

Would you mind telling us which NTSB report you're quoting?  There're kind of a lot.

@Vikki-formerlySean, I have updated the post with the information. Thanks!

You're very welcome!  :-)

One other thing - you said you were reading the Powerplant Group Chairman's factual report, but the quoted passage is from the final accident report.

The wording in the powerplant report: "No evidence of pre-impact failure was found. Evaluation of the propeller damage determined that neither propeller was feathered at impact. Witness marks provided data from which estimated propeller blade angles at the time of impact could be derived. The marks indicated that the left powerplant was producing low to moderate power and the right propeller was producing moderate power at the time of impact."

Note that the report says "derived from witness marks on the preload plates", so the investigators did not use witness marks on propeller blades to determine the blade angle. This might have been possible, as scratches and the deformation of the blade tip do, to some extent, manifest blade angle, but you would need to take into account the speed at which the plane was travelling at the moment of the propeller strike. There is also the problem that propellers tend to get quite mangled in accidents such as this, so the endresult may be useless as evidence.
Now, the preload plate is more suitable for determining the angle of blade at the time of impact. It is a part at the root of the propeller, inside the propeller hub:

As the propeller hits the ground (or any solid(ish) object) the force of the impact is relayed all the way to the bottom of the blade, where the preload plate sits. This force will leave an indentation, a witness mark on the preload plate, and from this mark the investigators can determine the angle of the blade at the time of the impact, as the place of the mark will be specific to the blade angle.
Since it was briefly discussed in comments: A witness mark can be both a deliberate marking on a part, made to ensure proper installation for example, but it also means a mark induced by force during an accident or some other event:
Waywordradio.org: witness mark (thanks Chris)
In good old days one common witness mark the accident investigators were searching for, were the small scratches the gauge needle made on the dial during an impact. These witness marks pretty accurately showed what each gauge was reading at the moment the plane crashed if the impact was at a favourable angle.
Picture source: Propeller Owner's Manual - Harzell Propeller Inc.

I'm only going by that cutaway drawing and some assumptions about the mechanism, but it looks like by the time the force is transmitted to the preload plate, analysing the damage will be far simpler, a matter of a mark at an angle, rather than trying to decipher far worse damage

My understanding, from a manufacturing perspective, that witness marks are made in machined parts ahead of time and are used for assembly Quality Control, is there any reference you can find in terms of use of witness mark as an impact feature?

@crasic Here is a reference: https://www.waywordradio.org/witness_mark/
"generally, an intentional, accidental, or naturally occurring spot, line, groove, or other contrasting area that serves as an indicator of certain facts" ...
"in construction and manufacturing, a line, groove, score, notch, cut, or written indicator made on the surface of material to impart information, such as where to cut or join; in forensic investigation, a surface groove, smear, stain, abrasion or other feature that can serve as evidence."

@Jpe61, your example image is almost spot on. The NTSB report concerns a HC-E4N-3.

@BtureP I just picked a random one from the manual